1. Field of the Invention
This invention relates to a novel process for the production of a graphite intercalation compound and to a novel, heretofore synthetically unattainable graphite intercalation product.
More particularly, this invention relates to a method for the production of a graphite intercalation compound, which, by using a previously synthesized graphite intercalation compound as a raw material in the synthesis of the graphite intercalation compound aimed at, enables the time required for the synthesis to be notable shortened and confers upon the produced compound a structure unattainable by the conventional technique of synthesis and to a graphite intercalation compound possessing a novel intercalate.
2. Description of the Prior Art
The term "stage number" is used in specifically expressing the periodic superlattice structure of a graphite intercalation compound. This "stage number" indicates how often, in the graphite layers of a given graphite intercalation compound, those graphite layer surfaces carrying thereon the intercalate (otherwise known as "intercalant") regularly occur as expressed in terms of the number of intervening layers. For example, the "first stage" represents the case in which the intercalate is present on every graphite layer surface, the "second stage" represents the case in which the intercalate is present on every second graphite layer surface, and the third stage or more can be expressed in the same way. The term "stage structure" is used in referring generally to the graphite intercalation compound structures in which the intercalate is present periodically from the superlattice point of view.
The graphite intercalation compounds have been demonstrated to retain the chemical stability inherent in graphite and, at the same time, possess as high electroconductivity as metals. Thus, numerous studies are now under way on these compounds.
These studies have so far unveiled the fact that the graphite intercalation compounds have the qualities thereof determined by the particular kinds of intercalates present therein.
The graphite intercalation compounds are conveniently classified into acceptor type graphite intercalation compounds, donor type graphite intercalation compounds, and covalent bond type graphite intercalation compounds, depending on the kinds of substances intercalated therein.
The term "acceptor type graphite intercalation compound" refers generally to graphite intercalation compounds of a type such that substances intercalated therein are present between graphite layers in the form accepting electrons from graphite. For example, those graphite intercalation compounds which contain ferric chloride, cupric chloride, aluminum chloride, cobalt chloride, cupric bromide, bromine, etc. as their intercalates belongs to this type.
In contrast, graphite intercalation compounds of a type such that substances intercalated therein are present between graphite layers in the form donating electrons to graphite are generally referred to as the term "donor type graphite intercalation compound." Examples of this type are those graphite intercalation compounds which contain potassium, lithium, rubidium, cesium, etc. as their intercalates.
Graphite intercalation compounds of a type such that substances intercalated therein share covalent bonds with graphite such as graphite fluoride are generally referred to as the term "covalent bond type graphite intercalation compound."
In the donor type graphite intercalation compounds, those which use alkali metals such as, for example, potassium as their intercalates are found to possess improved electroconductivity but lack stability in the air. Thus, they are immediately decomposed when they are exposed to the air (Physical Review B., Vol. 25, p. 4583, 1982). It is reported that a graphite intercalation compound using antimony pentafluoride as its intercalate exhibits better electroconductivity than elementary copper. This compound similarly lacks stability in the air and, therefore, has a problem yet to be solved for the purpose of practical adoption (Bulletin of American Physical Society, Vol. 21, p. 262, 1976).
Those acceptor type graphite intercalation compounds which use metal chlorides, for example, as their intercalates possess electroconductivity nearly equivalent to the electroconductivity of most metals, though not superior to that of elementary copper, and retain stability even in the air. Particularly the graphite intercalation compound using cupric chloride as its intercalate is stable not only in the air but also in water. However, for cupric chloride to be intercalated into graphite, the reaction proceeds so slowly that some tens of days are required for completion of the reaction (Glossary of Lectures for the 11th Annual Meeting of the Carbon Society of Japan, p. 42, 1982). Because of the slowness of this reaction, quantity production of this particular species of compound proves to be substantially difficult.
Further, during the intercalation of nickel chloride between layers of graphite, the reactivity of this intercalation s greatly affected by the reaction temperature. When the reaction temperature is not higher than 500.degree. C., for example, it takes several weeks to several months for the reaction to be completed. Furthermore in this case, the chemical composition and structure of the graphite intercalation compound synthesized at any temperature in the range of 495.degree. to 690.degree. C. are equal. Even if the intercalation is effected at a temperature outside the range mentioned above, no more nickel chloride can be intercalated between layers of graphite than when the reaction is performed at a temperature in the range. The stage structure in this case is invariably that of the second stage. By this method, therefore, graphite intercalation compounds of the first stage obtained by many graphite intercalation compounds having metal chlorides such as, for example, ferric chloride or cupric chloride intercalated therein can not be obtained (Synthetic Metal, Vol. 3, p. 1, 1981).
It is reported that, during the intercalation of nickel chloride between layers of graphite, the synthesis carried out in such a manner that the chlorine pressure is kept about 7 kg/cm.sup.2 under the reaction conditions gives birth to a graphite intercalation compound possessing the first stage structure (Solid State Ionics, Vol. 9 and 10, 1983). This synthesis lacks feasibility by reason of safety because the reaction conditions involved are harsh particularly in the sense that chlorine, a highly corrosive gas, must be used at elevated temperatures under high pressure.
No successful production of a graphite intercalation compound using calcium chloride, barium chloride, or silver chloride as its intercalate has been reported in the art.